1. Field of the Invention
The present invention relates to a vehicle charging system, and in particular, to a vehicle charging system including a charger configured to be supplied with electric power from a power supply external to a vehicle for charging a vehicle-mounted power storage device.
2. Description of the Background Art
In an electric vehicle and a hybrid vehicle, it is under consideration to mount a plurality of power storage devices thereon to extend the distance that can be traveled without operating an engine (EV travel distance). When the plurality of power storage devices are mounted in this manner, electric power distribution to each power storage device is a problem.
Japanese Patent Laying-Open No. 2008-109840 discloses a power supply system for a vehicle on which a plurality of power storage devices are mounted. In this power supply system, a discharge share ratio calculation unit determines, for each of the plurality of power storage devices, a remaining electric power quantity before a state of charge (SOC) is reached with respect to which an allowable discharge electric power is restricted, and determines a discharge power share ratio according to a ratio of the remaining electric power quantity between the plurality of power storage devices.
A charge share ratio calculation unit determines, for each of the plurality of power storage devices, a chargeable quantity before SOC is reached with respect to which an allowable charge electric power is restricted, and determines a charge power share ratio according to a ratio of the chargeable quantity between the plurality of power storage devices. When electric power is supplied from the power supply system to a drive force generation unit, a plurality of converters are controlled according to the discharge power share ratio. When electric power is supplied from the drive force generation unit to the power supply system, the plurality of converters are controlled according to the charge power share ratio.
In recent years, in the hybrid vehicle, it is under consideration to configure a mounted power storage device to be externally chargeable as well. Such a vehicle will also be referred to as a plug-in vehicle hereinafter.
In order to implement the plug-in vehicle, it is desirable to increase the capacity of the power storage device and increase the amount of electric power that can be externally charged. In addition to the power supply system (the system for power running during operation of the vehicle and charge/discharge during regeneration) as disclosed in Japanese Patent Laying-Open No. 2008-109840, it is easy to mount a charger when the vehicle is externally charged. Such an additional charger is also referred to as an add-on charger.
Generally, a charger for a power storage device such as a battery often has a power saving function of anticipating that the charger may overheat and limiting charging power so as to prevent the overheating caused by an excessive current flowing through the charger. When the add-on charger whose charging power is limited by the power saving function returns to a normal state, however, care must be taken to prevent excessive electric power flowing through the add-on charger or an unstable state of the charging power caused by hunting and the like. Japanese Patent Laying-Open No. 2008-109840 described above does not disclose such a problem.